Acyuta refers to the infallible Lord Visnu, whose heart is always infallible. Because the devotees are attached to the infallible, they are called acyutatma

Expressions researched:
"Acyuta refers to the infallible Lord Viṣṇu, whose heart is always infallible. Because the devotees are attached to the infallible, they are called acyutātmā"

Srimad-Bhagavatam

SB Canto 7

All the devotees of Lord Kṛṣṇa are called acyutātmā because they follow in the footsteps of Prahlāda Mahārāja. Acyuta refers to the infallible Lord Viṣṇu, whose heart is always infallible. Because the devotees are attached to the infallible, they are called acyutātmā.

SB 7.1.48, Translation and Purport

Mahārāja Yudhiṣṭhira inquired: O my lord, Nārada Muni, why was there such enmity between Hiraṇyakaśipu and his beloved son Prahlāda Mahārāja? How did Prahlāda Mahārāja become such a great devotee of Lord Kṛṣṇa? Kindly explain this to me.

All the devotees of Lord Kṛṣṇa are called acyutātmā because they follow in the footsteps of Prahlāda Mahārāja. Acyuta refers to the infallible Lord Viṣṇu, whose heart is always infallible. Because the devotees are attached to the infallible, they are called acyutātmā.